Chip Fragmentation in the Milling of AZ91HP Magnesium Alloy

Abstract

This paper presents new approaches to safety assessment in the milling of magnesium alloy. The objective of the study is to determine the effect of milling parameters and end mill geometry on machining safety, defined as the minimum probability of chip self-ignition. The assessment of safety and effectiveness in the milling of magnesium must include analysis of chip fractions formed during the milling process. The paper presents the state of the art of magnesium alloy machinability in terms of chip formation (chip fragmentation). Furthermore, the paper investigates the correlation between the quantity of distinguished chip fractions and variations in the parameters vc and fz as well as in the rake angle γo. In addition, the results of the dimensions of individual chip fractions are reported. The study was conducted on AZ91HP magnesium cast alloy, and the milling process was performed using carbide tools with varying rake angles (γo = 5o and γo = 30o). It has been found that chip fragmentation increases by increasing the above parameters, i.e. the feed rate fz and the cutting speed vc. The observed chip fragmentation (the quantity of chip fractions) is lower at the tool rake angle γo = 30o. Finally, technological recommendations are formulated based on the quantity of chip fractions generated at particular settings. The results do not unequivocally demonstrate that chip dimensions increase or decrease by increasing the operational parameters of the milling process. In terms of their application, it is vital that machining processes be simultaneously effective and safe.